Tuesday, November 6, 2007

The Sahara is technically the world’s second largest desert after Antarctica. At over 9,000,000 square kilometres (3,500,000 sq mi), it covers most parts of northern Africa; an area stretching from the Red sea, including parts of the Mediterranean coasts, to the outskirts of the Atlantic ocean. It is almost as large as the United States, and is larger than Australia. Its name derives from an Arabic word meaning “desert”: “ṣaḥrā´” (صحراء); to refer to the Sahara as the ‘Sahara Desert’ is therefore a pleonasm.

According to a botanical criteria of Cap-Rey, the Sahara is comprised between the following:* at north: limits of the maturity of Phoenix dactylifera (date palm trees)* at south: southern limit of Cornucala monacantha (a Chenopodiaceae) or northern limit of the Cencrus biflorus (a Poaceae of the Sahel region).

According to climatic criteria:* at north: an isohyet of 100 mm annual precipitation.* at south: a limit described by an isohyet of 150 mm annual precipitation (keeping in mind that precipitation varies strongly from one year to another).

The Sahara has one of the harshest climates in the world. It has many strong winds that blow from the north-east. Sometimes on the border zones of the north and south, the desert will receive about 25 cm (10 in.) of rain a year. The rainfall happens very rarely, but when it does it is usually torrential when it occurs after long dry periods, which can last for years.